Eye versus hand effector-specificity in the parieto-frontal cortex and cerebellum in humans
The degree and distribution of effector-specific representations for saccade and reach movements in the human brain remain unclear, partly because overlapping regional activation and the limited temporal resolution of fMRI complicate the identification of effector-dependent signals. Using a cue-separated event-related fMRI paradigm, we examined cortical and cerebellar activity across three temporally separated phases: visual target encoding, movement planning, and movement execution in 19 adults. We combined conventional univariate analyses with multivariate analyses of spatial activity patterns to characterize overlapping and distinct neural activity associated with each effector. Univariate analyses revealed widespread overlap across parieto-frontal regions, alongside effector-dependent differences in the magnitude and distribution of activation. Reach-related activity was generally more extensive than saccade-related activity, particularly during planning, while execution revealed distinct patterns of effector-preferential activation across cortical and cerebellar regions. Despite overlapping activation, multivariate analyses identified distinguishable spatial activity patterns across cortical and cerebellar regions. These findings confirm that (1) separating sensorimotor phases improves the detection of effector-preferential signals across the brain, and (2) overlapping activation during eye and hand movements does not necessarily imply equivalent neural activity patterns. Instead, multivariate analyses reveal widespread effector-dependent differences, suggesting a greater degree of spatial differentiation between saccade- and reach-related activity across the human cortex and cerebellum than conventual activation analyses alone would indicate.